The quality of food products and other perishables are highly dependent on storage conditions such as the temperature and the storage time from production or packing until it finally reaches the end consumer. The deterioration processes are faster when the temperature is raised due to increasing biochemical or physical reaction rates, and therefore the quality of perishable goods declines more rapidly at high temperatures than at low temperatures.
Examples of perishable goods which need to be stored under conditions such that a particular temperature exposure limit is not exceeded or at least not exceeded for longer than a predetermined period of time, include fresh food products, chilled food products and food products that have been pre-cooked or processed by freezing, irradiation, partial cooking, freeze drying or steaming, including products being packages in vacuum packaging, MAP-packed packaging or other industrial packaging methods. Further examples of products which may need to be stored under appropriate temperature conditions are certain pharmaceuticals, e.g. insulin, vaccines and concentrated omega-3 products; certain nutraceuticals, e.g. supplement oils, e.g. fish oil, and vitamins; chemicals; veterinary products and certain cosmetics; which would otherwise deteriorate.
Currently date marking is the standard method applied for the insurance of storage quality. By date marking only, no information is given to the consumer or others about the storage conditions to which the product has been exposed; hence the purchasers of susceptible products are not able to determine whether the product has been stored under appropriate temperature conditions during the time of storage. Relying on date marking as a sole quality criterion presupposes that the perishable product has been stored under appropriate conditions throughout the entire storage period. To be on the safe side, producers of perishable goods often use date marking with a wide safety margin, hence products which are actually still suitable for consumption or use are often discarded.
Therefore, there is a continuing interest in the monitoring of the time and temperature to which storage sensitive products have been exposed in e.g. food, pharmaceutical and chemical distribution chains from factory to consumer.
By supplying a perishable product with a time-temperature indicator which follows the individual product from packing to sale, the producer, the grosser, the retailer and the consumer will have a better product control than they currently have. By the use of a time-temperature indicator which matches the characteristics of investigated products, the true shelf life of the products can be monitored, which means that discarding can be delayed until the applied time-temperature indicator has detected that storage conditions based on time and temperature have not been appropriate and/or exceeded.
In theory, time-temperature indicators may be classified as either partial history or full history indicators depending on their response mechanism. Partial history indicators will typically not respond unless a threshold temperature has been exceeded, while full history indicators typically respond independently of a temperature threshold and provides a cumulative response to the time and temperature to which the time-temperature indicator (and hence the product) has been exposed.
EP 505 449 (Tepnel Medical) discloses an example of a partial history time-temperature indicator comprising a fusible material such as polycaprolactone triol, polyethylene glycol C1-4 alkyl ether and polyvinyl alcohol, which flows when a given threshold temperature is exceeded and re-solidifies when exposed to temperatures below the same temperature. The fusible material flows in a substrate and an indicator system produces a physically detectable change in the substrate when the fusible material flows therein.
U.S. Pat. No. 7,290,925 (TimeTemp) discloses an example of a full history time-temperature indicator where the response given by the time-temperature indicator is easily read by the human eye, and in conjunction with a product it gives a measure of the storage conditions to which the product has been exposed by giving a cumulative response to time-temperature exposure.
The reliability of a time-temperature indicator depends to a large extent on the correlation of the time-temperature indicator response with that of reactions leading to quality loss. Unless the change in the rate with temperature of the time-temperature indicator system closely parallels the temperature dependence of the rate of quality detoriation of the monitored product, the system will not be able to accurately predict the shelf life remaining for a variable temperature distribution. Also, as the temperature dependence on quality detoriation may be different in different temperature intervals, the temperature dependency of the time-temperature indicator may in these cases advantageously be of a non-linear response.
Further, the response to time and temperature should be substantially irreversible to prevent the time-temperature indicator from being reset. It is also preferred that the time-temperature indicator is capable of indicating the time-temperature history within a wide temperature range. The indicator should also be conveniently activated so that pre-usage storage of the indicator is not a problem, and the response to time and temperature should be given in a visually and easily interpretable manner. Finally, and importantly, it should be non-toxic and not pose any threat to human health.
According to the present invention there is now provided a time-temperature indicator system useful for monitoring the time and temperature exposure of food and other products. The system provides improved time-temperature sensitivity within a wide temperature range and a response which better reflects that of the reactions leading to quality loss.